refactor(HasFab): add HasFab.java back

mastodon/src/main/java/org/joinmastodon/android/fragments/HasFab.java

@@ -0,0 +1,10 @@
+package org.joinmastodon.android.fragments;
+
+import android.view.View;
+
+public interface HasFab {
+	View getFab();
+	void showFab();
+	void hideFab();
+	boolean isScrolling();
+}